Analysis of a 28-nm CMOS Fast-Lock Bang-Bang Digital PLL With 220-fs RMS Jitter for Millimeter-Wave Communication

This article analyses and demonstrates a 22.5-27.7-GHz fast-lock low-phase-noise bang-bang digital phase-locked loop (PLL) for millimeter-wave (mm-wave) communication. A discrete-time PLL model, together with theoretical transfer functions, gives insight on the functionality of the automatic bandwidth control, on the effect of the gear-shift algorithm for fast lock and on the different noise contributions. The proposed gear-shift algorithm scales up the PLL bandwidth for faster acquisition and orderly reduces it for jitter performance. The PLL contains a digitally controlled oscillator (DCO) based on transformer feedback with a tunable source-bridged capacitor, which allows for a low phase noise (PN) over a wide tuning range (FoM of -184 dBc/Hz and FoM(T) of -191 dBc/Hz) and for a fine frequency resolution. The PLL occupies 0.09-mm(2) core area and exhibits 220 fs rms jitter while consuming 25 mW, giving FoM(RMS) of -239 dB. Its frequency acquisition time improves from 780 to 45 mu s with the gear-shift algorithm. For 60-GHz communication, with a frequency multiplication factor of 2.5, this PLL covers all six channels' frequencies of IEEE-802.11ad, allows a transmitter (TX) error vector magnitude (EVM) down to -35.9 dB assuming a TX signal to the noise-plus-distortion ratio (SNDR) of 40 dB, and, thus, is capable of supporting 256 quadrature amplitude modulation (QAM).